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TV won't turn on after a period of use

Hi there. I wondered if anyone could help. My mum really loves her TV and I’m trying to fix but, but no joy.

The issue is that if powering on for the first time - say the morning - it powers up fine. But if you were to accidentally turn it off once in use, you can’t then turn it back on again, it won’t power up. The red LED flashes a few times as if it’s trying to power up, stops for a moment, then does it again. It does this about three times. Then the LED just goes off (as if it were on, but it’s not - no picture, no sound).

If the TV is left in standby for about 20 minutes or unplugged, then you can then power it on again as normal.

I heard a power board could be the issue, so I got one today and the issues are the same. I guess I could have been unlucky and got another faulty board, but the seller claims it’s tested and if the problem is still there it’d point to something else.

Does anyone have any ideas on what I could try?

The model is LG 42LG70.

Thank you

Update (01/20/2022)

Block Image

I notice a few people have talked about power boards and provided images, so I am adding an image of the new one just in case of it's any of use.

[well that didn't work!]

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@hostile17 we are going to assume that the power board works. Quick ( and very abbreviated) FYI and how this may work. It is the power board that supplies the voltages to the different boards as well as the LCD panel, but it is the Main board that tells the power board when and what to turn on. In your TV’s case it is possible that on or more of the IC’s on the Main board overheat and fail and thus the TV does not turn on. Sometimes your can use Freeze spray and see if cooling down the IC’s allows the TV to turn back on, other time a FLIR will allow you to see hot/cold spots and possibly determine which part has failed. you could also measure the voltages from the mainboard to the power board to see if those are correct. You would have to measure ones when the TV is cold and turns on and then repeat when it is hot and no longer turns on. At this point I would try another Main board if you do not think you have the tools/skills to troubleshoot the board. Of course post some pictures of that board as well as the T-con board (smaller board that connects via ribbon cable to the main board) with your Question. Let’s see if we can find anything odd looking. You will have to edit your QUESTION to add those images. 在已经存在的问题里加入图片

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Hi @oldturkey03 ,

You're most probably right.

Looking at the service manual it appears that the main IC is known for having problems. Unless it is just in the translation that it needs to be replaced. See the boxes at the bottom of the flowchart - some neck twisting is involved ;-)

replacement mainboards (assuming they're the right ones) are approx. $US75

Maybe a fan might work

Cheers

由完成的

@jayeff awesome find. This should really narrow it down and give @hostile17 a good chance to fixing the TV. hostile17 download the service manual that jayeff linked to.

由完成的

Thank you @oldturkey03 and @jayeff for helping this random stranger, and his mum who is strangely attached to this TV. "I'll buy you a new one." She is not keen though, she likes this one though.

It's twelve years old, it's done great service if I do have to replace it.

This is pushing further out of my comfort zone, but I'll use this advice and learn. I'm now leaving her place for a bit, so this will be something I will pick up on in a few weeks when back here.

I will either come back with more questions... or hopefully be further to a solution and can say I fixed it.

Either way, sincere thanks.

由完成的

@hostile17 sounds good and great job "mum"! Don't let go of the TV yet and hopefully we can keep her favorite TV out of the landfill for a long time.

由完成的

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